map_object.c revision 281452 
1/*-
2 * Copyright 1996-1998 John D. Polstra.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 *
25 * $FreeBSD: stable/10/libexec/rtld-elf/map_object.c 281452 2015-04-12 06:43:13Z kib $
26 */
27
28#include <sys/param.h>
29#include <sys/mman.h>
30#include <sys/stat.h>
31
32#include <errno.h>
33#include <stddef.h>
34#include <stdlib.h>
35#include <string.h>
36#include <unistd.h>
37
38#include "debug.h"
39#include "rtld.h"
40
41static Elf_Ehdr *get_elf_header(int, const char *);
42static int convert_prot(int);	/* Elf flags -> mmap protection */
43static int convert_flags(int); /* Elf flags -> mmap flags */
44
45/*
46 * Map a shared object into memory.  The "fd" argument is a file descriptor,
47 * which must be open on the object and positioned at its beginning.
48 * The "path" argument is a pathname that is used only for error messages.
49 *
50 * The return value is a pointer to a newly-allocated Obj_Entry structure
51 * for the shared object.  Returns NULL on failure.
52 */
53Obj_Entry *
54map_object(int fd, const char *path, const struct stat *sb)
55{
56    Obj_Entry *obj;
57    Elf_Ehdr *hdr;
58    int i;
59    Elf_Phdr *phdr;
60    Elf_Phdr *phlimit;
61    Elf_Phdr **segs;
62    int nsegs;
63    Elf_Phdr *phdyn;
64    Elf_Phdr *phinterp;
65    Elf_Phdr *phtls;
66    caddr_t mapbase;
67    size_t mapsize;
68    Elf_Addr base_vaddr;
69    Elf_Addr base_vlimit;
70    caddr_t base_addr;
71    int base_flags;
72    Elf_Off data_offset;
73    Elf_Addr data_vaddr;
74    Elf_Addr data_vlimit;
75    caddr_t data_addr;
76    int data_prot;
77    int data_flags;
78    Elf_Addr clear_vaddr;
79    caddr_t clear_addr;
80    caddr_t clear_page;
81    Elf_Addr phdr_vaddr;
82    size_t nclear, phsize;
83    Elf_Addr bss_vaddr;
84    Elf_Addr bss_vlimit;
85    caddr_t bss_addr;
86    Elf_Word stack_flags;
87    Elf_Addr relro_page;
88    size_t relro_size;
89    Elf_Addr note_start;
90    Elf_Addr note_end;
91
92    hdr = get_elf_header(fd, path);
93    if (hdr == NULL)
94	return (NULL);
95
96    /*
97     * Scan the program header entries, and save key information.
98     *
99     * We expect that the loadable segments are ordered by load address.
100     */
101    phdr = (Elf_Phdr *) ((char *)hdr + hdr->e_phoff);
102    phsize  = hdr->e_phnum * sizeof (phdr[0]);
103    phlimit = phdr + hdr->e_phnum;
104    nsegs = -1;
105    phdyn = phinterp = phtls = NULL;
106    phdr_vaddr = 0;
107    relro_page = 0;
108    relro_size = 0;
109    note_start = 0;
110    note_end = 0;
111    segs = alloca(sizeof(segs[0]) * hdr->e_phnum);
112    stack_flags = RTLD_DEFAULT_STACK_PF_EXEC | PF_R | PF_W;
113    while (phdr < phlimit) {
114	switch (phdr->p_type) {
115
116	case PT_INTERP:
117	    phinterp = phdr;
118	    break;
119
120	case PT_LOAD:
121	    segs[++nsegs] = phdr;
122    	    if ((segs[nsegs]->p_align & (PAGE_SIZE - 1)) != 0) {
123		_rtld_error("%s: PT_LOAD segment %d not page-aligned",
124		    path, nsegs);
125		goto error;
126	    }
127	    break;
128
129	case PT_PHDR:
130	    phdr_vaddr = phdr->p_vaddr;
131	    phsize = phdr->p_memsz;
132	    break;
133
134	case PT_DYNAMIC:
135	    phdyn = phdr;
136	    break;
137
138	case PT_TLS:
139	    phtls = phdr;
140	    break;
141
142	case PT_GNU_STACK:
143	    stack_flags = phdr->p_flags;
144	    break;
145
146	case PT_GNU_RELRO:
147	    relro_page = phdr->p_vaddr;
148	    relro_size = phdr->p_memsz;
149	    break;
150
151	case PT_NOTE:
152	    if (phdr->p_offset > PAGE_SIZE ||
153	      phdr->p_offset + phdr->p_filesz > PAGE_SIZE)
154		break;
155	    note_start = (Elf_Addr)(char *)hdr + phdr->p_offset;
156	    note_end = note_start + phdr->p_filesz;
157	    break;
158	}
159
160	++phdr;
161    }
162    if (phdyn == NULL) {
163	_rtld_error("%s: object is not dynamically-linked", path);
164	goto error;
165    }
166
167    if (nsegs < 0) {
168	_rtld_error("%s: too few PT_LOAD segments", path);
169	goto error;
170    }
171
172    /*
173     * Map the entire address space of the object, to stake out our
174     * contiguous region, and to establish the base address for relocation.
175     */
176    base_vaddr = trunc_page(segs[0]->p_vaddr);
177    base_vlimit = round_page(segs[nsegs]->p_vaddr + segs[nsegs]->p_memsz);
178    mapsize = base_vlimit - base_vaddr;
179    base_addr = (caddr_t) base_vaddr;
180    base_flags = MAP_PRIVATE | MAP_ANON | MAP_NOCORE;
181    if (npagesizes > 1 && round_page(segs[0]->p_filesz) >= pagesizes[1])
182	base_flags |= MAP_ALIGNED_SUPER;
183
184    mapbase = mmap(base_addr, mapsize, PROT_NONE, base_flags, -1, 0);
185    if (mapbase == (caddr_t) -1) {
186	_rtld_error("%s: mmap of entire address space failed: %s",
187	  path, rtld_strerror(errno));
188	goto error;
189    }
190    if (base_addr != NULL && mapbase != base_addr) {
191	_rtld_error("%s: mmap returned wrong address: wanted %p, got %p",
192	  path, base_addr, mapbase);
193	goto error1;
194    }
195
196    for (i = 0; i <= nsegs; i++) {
197	/* Overlay the segment onto the proper region. */
198	data_offset = trunc_page(segs[i]->p_offset);
199	data_vaddr = trunc_page(segs[i]->p_vaddr);
200	data_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_filesz);
201	data_addr = mapbase + (data_vaddr - base_vaddr);
202	data_prot = convert_prot(segs[i]->p_flags);
203	data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED;
204	if (mmap(data_addr, data_vlimit - data_vaddr, data_prot,
205	  data_flags | MAP_PREFAULT_READ, fd, data_offset) == (caddr_t) -1) {
206	    _rtld_error("%s: mmap of data failed: %s", path,
207		rtld_strerror(errno));
208	    goto error1;
209	}
210
211	/* Do BSS setup */
212	if (segs[i]->p_filesz != segs[i]->p_memsz) {
213
214	    /* Clear any BSS in the last page of the segment. */
215	    clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz;
216	    clear_addr = mapbase + (clear_vaddr - base_vaddr);
217	    clear_page = mapbase + (trunc_page(clear_vaddr) - base_vaddr);
218
219	    if ((nclear = data_vlimit - clear_vaddr) > 0) {
220		/* Make sure the end of the segment is writable */
221		if ((data_prot & PROT_WRITE) == 0 && -1 ==
222		     mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE)) {
223			_rtld_error("%s: mprotect failed: %s", path,
224			    rtld_strerror(errno));
225			goto error1;
226		}
227
228		memset(clear_addr, 0, nclear);
229
230		/* Reset the data protection back */
231		if ((data_prot & PROT_WRITE) == 0)
232		    mprotect(clear_page, PAGE_SIZE, data_prot);
233	    }
234
235	    /* Overlay the BSS segment onto the proper region. */
236	    bss_vaddr = data_vlimit;
237	    bss_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_memsz);
238	    bss_addr = mapbase +  (bss_vaddr - base_vaddr);
239	    if (bss_vlimit > bss_vaddr) {	/* There is something to do */
240		if (mmap(bss_addr, bss_vlimit - bss_vaddr, data_prot,
241		    data_flags | MAP_ANON, -1, 0) == (caddr_t)-1) {
242		    _rtld_error("%s: mmap of bss failed: %s", path,
243			rtld_strerror(errno));
244		    goto error1;
245		}
246	    }
247	}
248
249	if (phdr_vaddr == 0 && data_offset <= hdr->e_phoff &&
250	  (data_vlimit - data_vaddr + data_offset) >=
251	  (hdr->e_phoff + hdr->e_phnum * sizeof (Elf_Phdr))) {
252	    phdr_vaddr = data_vaddr + hdr->e_phoff - data_offset;
253	}
254    }
255
256    obj = obj_new();
257    if (sb != NULL) {
258	obj->dev = sb->st_dev;
259	obj->ino = sb->st_ino;
260    }
261    obj->mapbase = mapbase;
262    obj->mapsize = mapsize;
263    obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) -
264      base_vaddr;
265    obj->vaddrbase = base_vaddr;
266    obj->relocbase = mapbase - base_vaddr;
267    obj->dynamic = (const Elf_Dyn *) (obj->relocbase + phdyn->p_vaddr);
268    if (hdr->e_entry != 0)
269	obj->entry = (caddr_t) (obj->relocbase + hdr->e_entry);
270    if (phdr_vaddr != 0) {
271	obj->phdr = (const Elf_Phdr *) (obj->relocbase + phdr_vaddr);
272    } else {
273	obj->phdr = malloc(phsize);
274	if (obj->phdr == NULL) {
275	    obj_free(obj);
276	    _rtld_error("%s: cannot allocate program header", path);
277	    goto error1;
278	}
279	memcpy((char *)obj->phdr, (char *)hdr + hdr->e_phoff, phsize);
280	obj->phdr_alloc = true;
281    }
282    obj->phsize = phsize;
283    if (phinterp != NULL)
284	obj->interp = (const char *) (obj->relocbase + phinterp->p_vaddr);
285    if (phtls != NULL) {
286	tls_dtv_generation++;
287	obj->tlsindex = ++tls_max_index;
288	obj->tlssize = phtls->p_memsz;
289	obj->tlsalign = phtls->p_align;
290	obj->tlsinitsize = phtls->p_filesz;
291	obj->tlsinit = mapbase + phtls->p_vaddr;
292    }
293    obj->stack_flags = stack_flags;
294    obj->relro_page = obj->relocbase + trunc_page(relro_page);
295    obj->relro_size = round_page(relro_size);
296    if (note_start < note_end)
297	digest_notes(obj, note_start, note_end);
298    munmap(hdr, PAGE_SIZE);
299    return (obj);
300
301error1:
302    munmap(mapbase, mapsize);
303error:
304    munmap(hdr, PAGE_SIZE);
305    return (NULL);
306}
307
308static Elf_Ehdr *
309get_elf_header(int fd, const char *path)
310{
311	Elf_Ehdr *hdr;
312
313	hdr = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_PRIVATE | MAP_PREFAULT_READ,
314	    fd, 0);
315	if (hdr == (Elf_Ehdr *)MAP_FAILED) {
316		_rtld_error("%s: read error: %s", path, rtld_strerror(errno));
317		return (NULL);
318	}
319
320	/* Make sure the file is valid */
321	if (!IS_ELF(*hdr)) {
322		_rtld_error("%s: invalid file format", path);
323		goto error;
324	}
325	if (hdr->e_ident[EI_CLASS] != ELF_TARG_CLASS ||
326	    hdr->e_ident[EI_DATA] != ELF_TARG_DATA) {
327		_rtld_error("%s: unsupported file layout", path);
328		goto error;
329	}
330	if (hdr->e_ident[EI_VERSION] != EV_CURRENT ||
331	    hdr->e_version != EV_CURRENT) {
332		_rtld_error("%s: unsupported file version", path);
333		goto error;
334	}
335	if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) {
336		_rtld_error("%s: unsupported file type", path);
337		goto error;
338	}
339	if (hdr->e_machine != ELF_TARG_MACH) {
340		_rtld_error("%s: unsupported machine", path);
341		goto error;
342	}
343
344	/*
345	 * We rely on the program header being in the first page.  This is
346	 * not strictly required by the ABI specification, but it seems to
347	 * always true in practice.  And, it simplifies things considerably.
348	 */
349	if (hdr->e_phentsize != sizeof(Elf_Phdr)) {
350		_rtld_error(
351	    "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path);
352		goto error;
353	}
354	if (hdr->e_phoff + hdr->e_phnum * sizeof(Elf_Phdr) >
355	    (size_t)PAGE_SIZE) {
356		_rtld_error("%s: program header too large", path);
357		goto error;
358	}
359	return (hdr);
360
361error:
362	munmap(hdr, PAGE_SIZE);
363	return (NULL);
364}
365
366void
367obj_free(Obj_Entry *obj)
368{
369    Objlist_Entry *elm;
370
371    if (obj->tls_done)
372	free_tls_offset(obj);
373    while (obj->needed != NULL) {
374	Needed_Entry *needed = obj->needed;
375	obj->needed = needed->next;
376	free(needed);
377    }
378    while (!STAILQ_EMPTY(&obj->names)) {
379	Name_Entry *entry = STAILQ_FIRST(&obj->names);
380	STAILQ_REMOVE_HEAD(&obj->names, link);
381	free(entry);
382    }
383    while (!STAILQ_EMPTY(&obj->dldags)) {
384	elm = STAILQ_FIRST(&obj->dldags);
385	STAILQ_REMOVE_HEAD(&obj->dldags, link);
386	free(elm);
387    }
388    while (!STAILQ_EMPTY(&obj->dagmembers)) {
389	elm = STAILQ_FIRST(&obj->dagmembers);
390	STAILQ_REMOVE_HEAD(&obj->dagmembers, link);
391	free(elm);
392    }
393    if (obj->vertab)
394	free(obj->vertab);
395    if (obj->origin_path)
396	free(obj->origin_path);
397    if (obj->z_origin)
398	free(obj->rpath);
399    if (obj->priv)
400	free(obj->priv);
401    if (obj->path)
402	free(obj->path);
403    if (obj->phdr_alloc)
404	free((void *)obj->phdr);
405    free(obj);
406}
407
408Obj_Entry *
409obj_new(void)
410{
411    Obj_Entry *obj;
412
413    obj = CNEW(Obj_Entry);
414    STAILQ_INIT(&obj->dldags);
415    STAILQ_INIT(&obj->dagmembers);
416    STAILQ_INIT(&obj->names);
417    return obj;
418}
419
420/*
421 * Given a set of ELF protection flags, return the corresponding protection
422 * flags for MMAP.
423 */
424static int
425convert_prot(int elfflags)
426{
427    int prot = 0;
428    if (elfflags & PF_R)
429	prot |= PROT_READ;
430    if (elfflags & PF_W)
431	prot |= PROT_WRITE;
432    if (elfflags & PF_X)
433	prot |= PROT_EXEC;
434    return prot;
435}
436
437static int
438convert_flags(int elfflags)
439{
440    int flags = MAP_PRIVATE; /* All mappings are private */
441
442    /*
443     * Readonly mappings are marked "MAP_NOCORE", because they can be
444     * reconstructed by a debugger.
445     */
446    if (!(elfflags & PF_W))
447	flags |= MAP_NOCORE;
448    return flags;
449}
450